Janus kinase 3 (JAK3) is an intracellular kinase involved in cytokine and antibody receptor signaling; it is frequently over-activated during the course of inflammatory autoimmune diseases. Therefore, suitable JAK3 inhibitors that modulate the overexpression of JAK3 may be potential agents for treating autoimmune diseases. Logically, it is of significant importance to develop a sensitive, precise, and rugged screening tool to select agents that modulate the over-activation of JAK3. Currently available screening ELISA tools use only the active site of JAK3. Generally, the assay employs the quantitative sandwich enzyme immunoassay technique. Briefly, antibody specific for JAK3 is pre-coated onto a microplate. Standards and samples are transferred into the wells and any JAK3 present is bound by the immobilized antibody. After removing any unbound substances, a biotin-conjugated antibody specific for JAK3 is added to the wells. Following a wash to remove any unbound avidin-enzyme reagent, a substrate solution is added to the wells and color develops in proportion to the amount of JAK3 bound in the initial step. Another technology utilizes an induced fit concept different from the classical 'lock and key model' of enzyme activity, in thatit was believed that the 3D structures of the enzyme active sites are continuously reshaped by interactions with their substrates/inhibitors. Overall, all currently available screening tools hav several common deficiencies including low sensitivity, requiring an external substrate, and requiring a radioactive detection. As part of our continued efforts in the research in immune- mediated disorders, we have been working on improving the screening technology for finding better JAK3 inhibitors; we herein present the novel screening kit under development. Briefly, the proposed JAK3 screening tool comprises the use of full-length JAK3, different from currently available in that only the active site of JAK3 is used. The advantages of our novel screening kit include (1) significantly lower background noise, (2) higher sensitivity, (3) no need for the external substrate, (4) no need to use the radioactive method, and (5) capable of measuring auto-(tyrosine)phosphorylation. The ultimate goal of this project is to manufacture and sell a significantly improved ELISA kit to new drug discovery companies for screening JAK3 inhibitors. The goal of this Phase I SBIR study is to show the feasibility of developing this novel kit as a superior commercial product. The specific aims for this SBIR Phase I study are: 1) To further prove the concept of using the full-length JAK3 antibody in the screening kit. 2) To test the kit o a number of compounds (positive control and potential compounds). We have published positive control as shown in Preliminary Studies section. In this SBIR Phase I study, we will synthesize at least 12 potential JAK3 inhibitors and purchase a series of compounds from purchased library to test the novel ELISA kit. 3) To validate that our screening method is accurate, precise, reproducible, and rugged. We will choose two suitable JAK3 inhibitors for the validation of our screening kit. 4) To compare and contrast between already existing technology and our new technology under development.